#define _CRT_SECURE_NO_WARNINGS 1
#include <stdio.h>
int main()
{
	int denominator = 1;
	double sum = 0;
	for (denominator = 1; denominator <= 100; denominator++)
	{
		if (denominator % 2 == 1)
		{
			sum += 1.0 / denominator;
		}
		else
		{
			sum -= 1.0 / denominator;
		}
	}
	printf("%lf", sum);
	return 0;
}